[T]he whole teaching and work of John was in preparation for Christ: just as it is the duty of the servant and of the under-craftsman to prepare the matter for the form which is accomplished by the head-craftsman. Now grace was to be conferred on men through Christ, according to John 1:17: “Grace and truth came through Jesus Christ.” Therefore the baptism of John did not confer grace, but only prepared the way for grace; and this in three ways: first, by John’s teaching, which led men to faith in Christ; secondly, by accustoming men to the rite of Christ’s baptism; thirdly, by penance, preparing men to receive the effect of Christ’s baptism. (
Summa Theologica of St. Thomas Aquinas, available at:
www.newadvent.org)